A chest percussor, or the technique of chest percussion, is used to loosen and clear thick mucus from the lungs in individuals with respiratory conditions like cystic fibrosis, COPD, or pneumonia. It involves rhythmically clapping the chest with cupped hands or a device to create vibrations that dislodge secretions, which are then moved towards larger airways to be expelled by coughing, often aided by postural drainage to use gravity to help with drainage.